Officials say the suicide bomber detonated his explosives near the Abul Fazel shrine as pilgrims gathered Tuesday to celebrate the Shi'ite festival of Ashura. More than 100 people were also wounded in the blast.

Eyewitnesses say that some hospitals in the area are overwhelmed with the number of wounded.

"I took this wounded person to this emergency hospital for treatment, but here, there is not treatment, and no one cares that I have been waiting here for two hours," said Kabul resident Shah Hussein. "I need to take this person to another hospital."

Authorities say the number of casualties is expected to rise.

Meanwhile, officials say a second explosion targeted a shrine in the northern city of Mazar-e-Sharif, killing four people. It is not clear whether Shi'ites were also the target of the second attack.

The Taliban released a statement on Tuesday saying it did not plan the attacks, calling them "cruel and indiscriminate" and blaming them on the "invading enemy."

The 10-day Ashura festival, which reaches its peak on Tuesday, is the most significant holiday for Shi'ite Muslims. It marks the death of Imam Hussein, the grandson of the Prophet Muhammad.

Afghan President Hamid Karzai immediately condemned the bombing, saying it was the first time a terrorist attack has taken place on "such an important religious day in Afghanistan."

Attacks between Afghanistan's Sunni citizens and minority Shi'ite population have been rare in recent years. Attacks between the two groups are more frequent in neighboring Pakistan.

Officials also said three people were wounded Tuesday when a bomb hidden in a motorcycle exploded in the southern city of Kandahar. The attack did not take place near any building of worship.

The attacks come a day after world leaders gathered in the German city of Bonn to discuss Afghanistan's future as international combat troops prepare to leave the country.

President Karzai told the conference that after the withdrawal of NATO troops from his country in 2014, Afghanistan will still need international help for at least another decade.

Pakistan, considered vital to any prospect of stability in Afghanistan, boycotted the one-day meeting in response to a cross-border attack by NATO late last month that killed 24 Pakistani soldiers.